In general, in machining tools, machining is implemented by relative rotation between a workpiece and a tool, the workpiece may be disposed, for example, on a chuck and rotary table, and a gear may be used as a transmission element.
In particular, transmission by gears has a characteristic, heat generation.
Further, it is required to rotate the spindle at high, medium, and low rotation speed, in accordance with how the workpiece will be machined. For example, the spindle may be rotated at a high or medium speed in simple turning of the outer circumference of the workpiece and may be rotated at a low speed when machining a key groove or a pin hole etc.
As described above, when the spindle is rotated at a high or medium speed, the spindle may function as a main shaft, in which backlash may be generated, but it is not necessary to remove the backlash.
Further, accurate rotation is necessary when indexing or milling the workpiece disposed on the spindle, and particularly, forward rotation and backward rotation may be repeated and the backlash should be removed for precision machining.
However, as described above, when multi-machining is applied to one workpiece, for example, when machining and milling of the outer circumference are performed, it is required first to rotate the spindle at a high speed and it is required to precisely rotate the spindle at a low speed for milling; however, the spindles of the related art can perform any one function in selection of a high speed or a low speed, such that the multi-machining cannot be performed.
Further, when a spindle (for example, a rotary table) that can be precisely rotated, with backlash removed, is rotated at a high speed, more heat is generated by the operation of gears, such that it is difficult to smoothly machine the workpiece.